1. Field of Invention
The present invention relates to a quantitative analysis of a functional group on the surface of a solid material and, more particularly, to a quantitative analysis of a functional group on the surface of a solid material based on acid-base titration.
2. Related Prior Art
Carbon nano-tubes are a new material. The carbon nano-tubes are however not directly used after they are made because they tend to tangle with one another to form masses. To distribute the carbon nano-tubes evenly in a solution or another material, they must be subjected to a chemical process to produce a functional group on their surfaces. Generally, nitric acid or sulfuric acid is used to produce carboxylic group and/or hydroxylic group on the surfaces of the carbon nano-tubes to provide the carbon nano-tubes with affinity for a dissolvent so that the carbon nano-tubes can be suspended and distributed in the dissolvent evenly. Then, the functional groups can be bonded to another chemical material. Thus, the carbon nano-tubes are suitable for various uses. The amount of the functional group on the surfaces of the carbon nano-tubes determines the amount of the chemical material that can be bonded to the carbon nano-tubes. Therefore, it is necessary to execute a quantitative analysis for the functional group.
Conventional quantitative analysis for the carboxylic group on the surfaces of the carbon nano-tubes are based on the acid-base titration. The conventional quantitative analysis is however complicated because the carbon nano-tubes possess special properties.
For example, as set forth in Equation (1), a first number (a) of moles of carboxylic group (—COOH) included in carbon nano-tubes (“CNT”) is reacted with a second number (b) of moles of sodium hydrogen carbonate (NaHCO3) to produce the first number (a) of moles of (H2CO3), leaving the second number minus the first number (b−a) of moles of sodium hydrogen carbonate. By sucking filtration, the carbon nano-tubes are separated from the solution. After the separation, as set forth in Equation (2), the second number (b) of moles of hydrochloric acid (HCl) is introduced into the sodium hydrogen carbonate solution so that the remaining sodium hydrogen carbonate is turned into the second number minus the first number (b−a) of moles of sodium chloride (NaCl) and the second number (2) of moles of carbonic acid, leaving the first number (a) of moles of hydrochloric acid. As set forth in Equation (3), by heating or introduction of nitrogen, the carbonic acid is turned into carbon dioxide (CO2) that escapes from the solution. Then, sodium hydroxide (NaOH) is used for acid-base titration of the first number (a) of moles of hydrochloric acid. From the fact that the first number of moles of sodium hydroxide is used for the titration, it is learned that the amount of the carboxylic group is the first number (a) of moles.
The foregoing process takes a long period of time. In particular, the separation of the carbon nano-tubes from the solution takes a long period of time for several reasons. Firstly, the size of the carbon nano-tubes is in the order of a nanometer and requires a filtration film with very small bores. Secondly, the very small bores of the filtration film could easily be blocked by the carbon nano-tubes. Thirdly, the acid-base titration is not sensitive, the carbon nano-tubes do not include a lot of carboxylic group, and it requires a lot of carbon nano-tubes for experiment. Therefore, the conventional quantitative analysis takes a long period of time and requires a lot of samples.aCNT—COOH+bNaHCO3→aCNT—COONa+aH2CO3+(b−a)NaHCO3  (1)aH2CO3+(b−a)NaHCO3+bHCl→bH2CO3+aHCl+(b−a)NaCl  (2)bH2CO3+aHCl+heat→bCO2↑+bH2O+aHCl  (3)
For example, 1 mole of carboxylic group included in carbon nano-tubes is reacted with 5 moles of sodium hydrogen carbonate to produce 1 mole of carbon-nano-tubes-sodium carboxylate, 4 moles of sodium hydrogen carbonate and 1 mole of carbonic acid. By sucking filtration, the carbon nano-tubes are separated from the solution. 5 moles of hydrochloric acid are introduced into the sodium hydrogen carbonate solution to produce 4 moles of sodium chloride and 5 moles of carbonic acid, with 1 mole of hydrochloric acid left. By heating, the carbonic acid is turned into carbon dioxide that escapes from the solution. Now, the solution contains 4 moles of sodium chloride and 1 mole of hydrochloric acid. Then, sodium hydroxide is used for acid-base titration of the 1 mole of hydrochloric acid that is left. From the fact that the amount of the sodium hydroxide used for the titration is 1 mole, it is learned that the amount of the carboxylic group is 1 mole.
In the conventional quantitative analysis, the amount of the sodium hydrogen carbonate must be excessive to hold the equations. Therefore, estimation must be done before the experiment. For example, 1 gram of carbon nano-tubes is used. For convenience of calculation, it is assumed that this 1 gram of carbon nano-tubes contains 100% of carboxylic group (—COOH) although the percentage cannot be 100%. 1 gram of —COOH is about 0.02222 mole. There must be provided an excessive amount of sodium hydrogen carbonate. For example, 100 ml of 0.5 N sodium hydrogen carbonate solution contains 0.05 mole of sodium hydrogen carbonate that is excessive. In addition, the carbon nano-tubes cannot contain 100% of —COOH. Evidenced by available documents, the carbon nano-tubes do not contain more than 10% of —COOH. However, should the amount of the carboxylic group be inadequate, errors such as errors of the amount of the sodium hydrogen carbonate and errors of the amount of the hydrochloric acid solution, the amount of the sodium hydrogen carbonate or the amount of the hydrochloric acid solution could be larger than the amount of the carboxylic group, and the carboxylic group could not be quantitatively analyzed. That is, the detection limit in the conventional acid-base titration is not low enough to conduct the quantitative analysis of a small amount of the carboxylic group. It is possible to make some progress such as conducting the experiment again to reduce the amount of the sodium hydrogen carbonate and increase the amount of the carbon nano-tubes, but the progress is limited.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.